Set a large skillet over medium-high heat. When it is sizzling hot, sprinkle it with 2 teaspoons salt, and at once add the meat pieces. Brown well on all sides. Season the meat with pepper, and turn into a bowl. Add the oil to the skillet and saute the onion for about 3 minutes; then turn into the slow-cooker. Swirl the water in the still hot skillet and scrape up the pan juices. Turn into the slow-cooker with the meat. Cover and cook on Low for 8 to 10 hours, or until the meat is very tender.

BEFORE SERVING:
In meduim skillet, over medium-high heat, saute the mushroom slices in 1 or 2 tablespoons of fat skimmed from the cooking liquid; stir constantly for about 5 minutes, when excess liquid has evaporated. Add 1/8 teaspoon salt. Arrange the short ribs on a heated serving platter and turn the cooking liquid into the mushroom skillet. Simmer, scraping up the pan juices, until the sauce is reduced and thickened. Remove skillet from the heat. Stir in the sour cream; return to the heat just long enough to thoroughly warm the sauce. Then pour over the meat and sprinkle with parsley.